Undead won't necessarily be worthless since you can literally poison healing potions, and poison abilities, while not quite as good normal healing abilities, are still available. It might be a bit more difficult to find poison than normal healing potions, but you will also heal from poison the enemies try to use on you so it balances out.
Of course, I'm assuming Larian will make player undead characters keep with the trend of having all undead, even bare skeletons, heal from poison instead of just ignoring the damage. So pretty much they'll have the zombie trait.
